三维起伏地形下宽角地震资料逆时偏移成像及应用

The basin-mountain coupling region in the western China has significant tectonic and dynamic effects, and it is rich in mineral resources and generally has strong and undulating topographic conditions at the same time. The seismic wide-angle reflection/refraction method is an important way to detect the crustal structure, while the reverse time migration imaging method is an important means to reveal the fine structure of the crust. In view of the fact that the imaging accuracy of the traditional reverse time migration imaging method for the wide-angle seismic data is limited by the undulating surface topography and complex media composition, so it is critical for the accurate reconstruction of the crust and upper mantle structure to carry out the study of the high-precision reverse time migration imaging method for wide-angle seismic data under the undulating surface. This study intends to develop an accurate inverse time migration method for wide-angle seismic data that perfectly matches the undulating terrain. The concept of generalized curvilinear coordinates in hydromechanics is introduced, and then the irregular surface of Cartesian coordinate system is mapped to a regular plane of generalized curvilinear coordinate system. The wave equation of the generalized curvilinear coordinate system is constructed and its finite difference decomposition method in the center format is developed, and then the inverse time migration imaging method is performed. We try to apply this method to the processing and interpretation of three dimensional wide-angle seismic data in eastern Kunlun of the Qinghai-Tibet Plateau, in order to reavealing the fine features of the regional crust structure, and thus enhancing the understanding of the crust deformation mechanism and dynamics of the northeastern Tibetan Plateau.

中国西部构造地貌复杂，盆山耦合显著，油气矿产资源丰富，但地形起伏剧烈多变。地震宽角反射/折射是探测地壳结构的重要方法，逆时偏移成像技术是揭示地壳精细结构特征的重要手段。由于传统的宽角资料逆时偏移成像方法受起伏地表地形和复杂介质组成等限制，成像精度较低，因此开展起伏地表条件下宽角地震数据的高精度逆时偏移成像方法研究，对于准确重建地壳上地幔结构至关重要。本项目拟发展一种与起伏地形完全匹配的宽角地震数据精确逆时偏移成像方法：引入流体力学中广义曲线坐标系的概念，将笛卡尔坐标系的非规则表面映射为广义曲线坐标系的规则平面，构造广义曲线坐标系的波动方程并发展其中心格式的有限差分解法，进而开展逆时偏移成像。尝试将该方法应用于青藏高原东昆仑三维宽角地震资料的处理解释，揭示区域地壳结构的精细特征，进而增进对青藏高原东北缘地壳变形机制和动力学的理解。

项目围绕地震波传播与成像方法研究以及中国典型构造域壳幔结构与流变性特征，开展了相关研究，获得如下主要成果：.（1）地震波传播与偏移成像方法研究；总结了远震波场正演模拟方法及应用情况，重点讨论了应用广泛的混合法；总计了近地表层析成像方法，包括基于高频近似理论的走时成像方法和有限频层析成像方法；发展了基于弹性波波场分解的互相关型最小二乘逆时偏移成像，显著提高了成像的精度；总结了短周期密集台阵被动源地震探测技术研究进展，重点讨论了在地壳结构研究和微震定位检测等方面的研究进展。.（2）在中国典型构造域开展了壳幔结构与各向异性特征研究；发现了胶东地区五莲断裂带岩石圈保存了三叠纪陆陆碰撞的化石各向异性，可能是华北华南的缝合带；青藏高原东北缘大部分区域SKS、Pms快波方向与地表构造走向相一致，暗示青藏高原东北缘以岩石圈垂直连贯变形为主，地壳上地幔相互耦合；钦杭成矿带和武夷山成矿带上地壳P波速度的不同，基底深度以及断裂性质的差异反映了两个成矿带深部成矿背景的差异，可能是造成两个成矿带成矿差异的主要控制因素。